In connection with manufacturing processes for producing semiconductor devices, a variety of techniques and processes are used which require the use of reactive gasses. One such common process is chemical vapor deposition (CVD) which is a thin film growth process wherein very high quality films are deposited onto a heated substrate. CVD processes are widely used for forming various layers during integrated circuit fabrication. For example, CVD processes have long been used for deposition of polysilicon, tungsten, silicon nitride, silicon oxynitride and various forms of silicon dioxide. CVD processes are also coming into use for deposition of conductive materials such as aluminum, metal sicilicides, and titanium nitride. CVD processes generally involve a decomposition of a precursor gas mixture, at the surface of the heated substrate, to form components which are the chemical precursors of the desired film composition. For example, polysilicon can be grown by decomposition of dichlorosilane. The CVD process is carried out in a sealed container which is evacuated before the selective introduction of reactive gases. These reactive gases are typically introduced in a serial manner to effect successive process steps. Typically, the reactive gases are delivered to the chamber from individual sources through a series of conduits and valves, which, in many cases result in each of the gases flowing through a single conduit that feeds the gas into the chamber. In many cases, the gases, if mixed, are potentially explosive. In other cases, the admixing of a small amount of residual gas from a prior process into the mainstream of gas flowing into the chamber at the beginning of a second process may result in contamination of the chamber which in turn affects the process and the ultimate quality of the semiconductor devices produced thereby.
Thus, there is a clear need in the art to provide better flow control of reactive, process gases into processing chambers in order to reduce the possibility that even small amounts of incompatible gases may be mixed together or simultaneously introduced into a processing chamber such that the chamber becomes contaminated. The present invention is intended to satisfy this need.